Research on high efficiency and retarded autogenous mud acid for plugging removal in a sandstone reservoir—Example of Bai 823 well area.

Acidification, as an effective measure to remove blockages and restore oil well productivity, has received widespread concern. However, conventional acid systems can only be used to unblock near‐wellbore zones and are difficult to act on far‐wellbore reservoirs. In this article, scanning electron microscope, energy‐dispersive X‐ray spectroscope, and X‐ray diffractometer were used to analyze the blockages in the Bai 823 well area, and it was determined that their main components were CaCO3 and FeCO3, which provided the basis for the construction of the unblocking formula. Then, the acid dissolution experiments on the plugging materials showed that the dissolution rate of 10% HCl can reach more than 85% for the scale sample; the acid dissolution experiments on the rock sample showed that the autogenous mud acid has better dissolution performance and better retardation performance for the rock sample, and the effective action time is longer, so it can be used for deeper unplugging of the reservoir. Finally, the process parameters such as the optimal acid concentration, acid dosage, and discharge volume were optimized by establishing the fracture‐matrix acid flow reaction model. Research results indicate that the autogenous mud acid can act on the blockage in the far‐wellbore area to improve the acidification effect. [ABSTRACT FROM AUTHOR]